1. Field of the Invention
The present invention relates to a robot controller for use in a robot system in which robot controllers are connected with one another through a communication path, and more particularly to a robot controller for use in a robot system for performing a synchronously cooperative operation by a plurality of robots.
2. Description of the Related Art
There is known a robot control system in which a plurality of robot controllers are connected through a communication path for performing a synchronously cooperative operation by a plurality of robots respectively controlled by the robot controllers. In such a system, when one robot is to be stopped for a certain cause, it is necessary to stop the other robots in performing the synchronously cooperative operation. Since a plurality of robots operate in synchronous cooperation, if one robot is stopped and the other robots continues the synchronously cooperative operation, the robots may cause interferences or fail to complete a part of the operation. Therefore, in the conventional robot control system, an emergency stop signal is issued from an upper PLC (programmable logic controller) to all the robots to be stopped immediately.
There are generally known different types of methods for stopping a robot. For example, in stopping a robot for a cause of an input of a hold signal, there are known (1) a deceleration stop of stopping the robot with an execution of acceleration/deceleration processing so as not to exert an excessive load on a robot mechanism; (2) a controlled stop of stopping a robot with an execution of the acceleration/deceleration processing and also a shut off of an excitation of servo motors; and (3) an immediate stop of stopping a robot by immediately shut off servo amplifiers by an emergency stop signal.
In the above system for controlling a plurality of robots, the above method (3) of immediate stop which effects the smallest slowdown amount is adopted to minimize the relative positional displacement of the robots in stopping.
The above immediate stop, however, had better be avoided since a large load is exerted on the robot mechanism. If all of the robots in performing the synchronously cooperative operation are stopped by the method of immediate stop when one of the robots is to be stopped for a certain cause in the above robot control system, a frequency of the immediate stop of the robots is made larger to be unpreferable. Depending on a cause for stop, it is preferable to stop the robots according to the method (1) of deceleration stop or the method (2) of controlled stop.
In stopping the robots in synchronously cooperative operation, it is necessary to stop all of the robots in synchronously cooperative operation by the same method of stopping to maintain the synchronous motion since different stopping methods cause differences between motion amounts of the respective robots so that a considerable disagreement is caused on the relative positions of the stopped robots with respect to the relative positions of the robots in synchronously cooperative operation to make a problem on the robot operation. For example, in the case of transferring an object by a plurality of robots in synchronous cooperation, there is a possibility of dropping the object by the disagreement of the relative positions of the robots.
According to an aspect of the present invention, a robot controller comprises: storing means for storing assignment information on types of stopping procedure assigned for each of a plurality of causes for stopping the robot; detecting means for detecting a first cause for stopping occurred in the robot associated with the robot controller; designating means for designating a first type of stopping procedure based on the detected first cause for stopping and the assignment information stored in the storing means; sending means for sending identification information on the designated first type of stop procedure to another robot controller through the communication path; receiving means for receiving identification information on a second type of stop procedure sent from another robot controller through the communication path; and determining means for determining a type of the procedure of stopping the associated robot based on the identification information on the first type of stopping procedure or the identification information on the second type of stopping procedure.
In place of sending and receiving the identification information on the type of stop procedure, the sending means may send identification information on the detected first cause for stopping to another robot controller through the communication path, and receiving means may receive identification information on a second cause for stopping occurred in a robot associated with another robot controller sent from another robot controller through the communication path and designating a second type of stop procedure based on the assignment information stored in the storing means.
The robot controller may further comprise specifying means for specifying one or more other robots to be stopped simultaneously with the associated robot when the first cause occurs. In this case, the sending means may send identification information on the first type of stop procedure or the first cause for stopping to one or more other robot controllers of the specified one or more other robots through the communication path, and the receiving means may receive identification information on a second type of stop procedure or a second cause for stopping from the one or more other robot controllers through the communication path.
The robot controller may further comprise means for sending and receiving information for performing a synchronized or cooperative operation. through the communication path, and means for enabling the determining means only when the associated robot is in performing a synchronized or cooperative operation with another robot.
The causes for stopping the robot may include an emergency stop command inputted in the robot and an alarm occurred in the robot, and the types of stopping procedure may be classified by whether or not a power supply is shut off and/or whether or not motors for driving the robot are subjected to acceleration/deceleration processing.